**8. Mechanism of action of biopesticides**

Biopesticides have a variety of distinct modes of action that are distinct from one another and may be used in various settings, including agriculture. Through a variety of mechanisms, including parasitism, antibiosis, and predation, among others, microorganisms generate pesticides that are harmful to humans and animals. Botanical pesticides have been shown to be very effective since they kill insects while also interfering with the development of diseases. Prey is killed as a result of the attack by being parasitized or poisoned, which leads them to die as a result of the attack. Pests are attracted to the treatment area as a consequence of the application of the treatment, which results in the pests being killed or sterilized (see **Figure 3**). Extracts from plants belonging to the Asteraceae family have been reported to inhibit hyphal growth and induce structural modifications in the mycelia of plant pathogenic fungi [112]. *Asteraceae* plants contain compounds such as flavonoids, coumarin alkaloids, and terpenoids, leading to absolute fungal toxicity. Some compounds lead to changes in the cell wall as well as the morphology of cellular organelles [113]. As a result, when bioactive chemicals come into contact with fungal cell membranes, they may induce partitioning and penetration, which will allow the contents of the cell to escape via a hole created by this partitioning. In addition, it has been shown that the separation of the cytoplasmic membrane induced by plant bioactive substances results in the destruction of intracellular components and the growth of cells, ultimately resulting in the death of the cells [114].

There are different types of biopesticides, including sabadilla, pyrethrum, azadirachtin, and fluoroacetate that show different mechanisms of action against pests. For example, the alkaloid toxin of sabadilla significantly caused the loss of nerve cell membrane mechanism by affecting the nerve cell membrane of insects. It was found that sabadilla could kill most insects immediately after its use, but a few could survive up to few days in a state of paralysis before dying [115]. In addition,

**Figure 3.**

*The general mechanism of action of nano-biopesticides for pest insect management. This figure is reproduced from Mossa, [111].*

the emerging evidence revealed that a low dose of pyrethrins significantly causes the immediate death of insects. For humans and warm-blooded animals, pyrethrins are not toxic. Allergic responses to humans, however, are frequent. It may cause a rash, and inhaling the dust can lead to headaches and illness. By altering the process of sodium and potassium ion exchanges in insect nerve fibers, pyrethrins exert their deadly effects by inhibiting the normal transmission of nerve impulses. The insecticides containing pyrethrin work very quickly and produce paralysis in the insects very quickly. But many insects can swiftly metabolize (break down) pyrethrins in spite of their acute toxicity. However, piperonyl butoxide (PBO) and pyrethrin could be used as combined therapy against these insects [116]**.**

A recently reported study revealed that administration of azadirachtin to third instar larvae significantly reduces food consumption compared to control [117]. But, its antifeedant activity surely depends on the insect species and dose concentration [118]. It was reported that the inhibition of feeding behaviors after azadirachtin dose from stimulation of deterrent receptors was coupled with sugar receptors that lead to food restriction, starvation, and bad nutrition [119]. Recently, various studies have demonstrated the weight loss behavior of azadirachtin in different insects, including *Spodoptera eridania*, *Periplaneta americana*, *Drosophila melanogaster,* and *Helicoverpa armigera* [117, 120]. The pesticide mechanism of action of fluoroacetate is well known; it was reported that after ingestion of fluoroacetate by insects, it converted into fluoroacetyl-CoA and after that, into fluorocitric acid. However, the structure analogue (fluorocitric acid) to citric acid blocked the activity of an enzyme that was involved in the conversion of citric acid to cis-aconitic acid resulting in the energy production method being stopped. Due to the accumulation of citric acid inside the cell, the concentration of α-ketoglutaric acid, calcium, and glutamic acid reduced that resulting affected the nervous system of the insect because the nervous system is very sensitive to these acids, especially glutamic acid which is an essential neurotransmitter [115]. When bugs are exposed to insecticides such as allicin, which may be found in garlic bulbs (*A. sativum*),

*Nano-Biopesticides as an Emerging Technology for Pest Management DOI: http://dx.doi.org/10.5772/intechopen.101285*

they suffocate and die. When applied to insects, allicin acts by interfering with the neurotransmitter receptors in their nervous systems. Suffocation is caused by substances such as allicin. Phytotoxins and terpenoids biochemically interact with insects via hydrophobic and ionic interactions. In addition, a large number of proteins are targeted and destroyed, resulting in physiological failure and degeneration. Plant extracts and essential oils include a range of compounds that may interact with an insect's nervous system and coordination, resulting in the insect's death as a consequence of the disruption produced by this contact [121].
